Integrated circuits are made on thin wafers (e.g., silicon, silicon carbide, sapphire, etc.) and include a plurality of contacts to interface with other circuits and devices. To facilitate coupling integrated circuits into electronic systems and protect them from the environment, the integrated circuits are attached to a substrate (e.g., a lead frame) and are then encapsulated into a mold (e.g., epoxy resin) that includes one or more electrical contacts (e.g., leads, solder balls, bumps, contacts, etc).
To encapsulate integrated circuits, one or more semiconductor devices attached to a lead frame are clamped at high pressures (e.g., 2500-3000 psi) into a mold chase having channels in communication with one or more gates. Generally, the mold chase is formed by clamping two mold bases together with a mold press. The mold chase includes cells with one or more corresponding integrated circuits of the lead frame contained therein. The mold chase is clamped at high pressure to prevent a liquid mold compound injected into the mold chase from bleeding out of cells contained therein.
A solid mold compound is supplied to the mold chase. A plunger applies pressure to the mold compound, causing the solid mold compound to convert into a liquid mold compound. The pressure from the plunger forces the liquid mold compound into the channels of the mold chase such that the liquid mold fills the cells of the mold chase via the gates associated with the channels. The liquid mold flows into the cells of the mold chase and fills the same to thereby encapsulate the integrated circuits of the lead frame. After a time, the liquid mold within the cells cures to form rigid housing(s) over the lead frame(s) and the associated integrated circuit(s).
In conventional mold systems, a main cylinder provides a clamping pressure to center the mold chase. Newer mold systems include a main cylinder and auxiliary cylinders that provide clamping pressure to one or more sides. The mold chases may also include support structures (e.g. pedestals) on one or more surfaces. To distribute clamping pressure in such mold chases, shimming of up to 0.2 mm may be inserted between the support structures.